About two songs into a Kenny Chesney show, gunshots began to ring out. Panicked concert-goers, who a few moments ago earlier were gleefully singing along with the famous country crooner, were now running for their lives.

A similar scene unfolded in Las Vegas last year — a country concert where 58 were killed and another 851 were wounded — and served as an elaborate training scenario Tuesday morning aimed at teaching scores of law enforcement officers from around the San Gabriel Valley, along with emergency room staff members at Pomona Valley Hospital at the Fairground in Pomona.

SWAT, fire and paramedics from Pomona, West Covina, Covina, Glendora and other nearby cities participated in the special training that mimicked the events of the Route 91 Harvest music festival last October, when a gunman opened fire, killing 58 people and wounding hundreds, many of them from Southern California.

“History is our best teacher and we need to learn from these situations,” Pomona police Sgt. Ryan Rodriguez told about 100 volunteers before they made their way into the grandstand, where the mass shooting training was set to take place.

A victim looks up at SWAT officers as they mobilize during an active shooter training drill at Fairplex in Pomona, CA., Tuesday, April 24, 2018. The multi-agency scenario mimicked the mass shooting event in Las Vegas last October. (Staff photo by Jennifer Cappuccio Maher, Inland Valley Daily Bulletin/SCNG)

Victims hide in the grandstands as SWAT officers search for the shooter during an active shooter training drill at Fairplex in Pomona, CA., Tuesday, April 24, 2018. The multi-agency scenario mimicked the mass shooting event in Las Vegas last October. (Staff photo by Jennifer Cappuccio Maher, Inland Valley Daily Bulletin/SCNG)

A victim is helped into the back of a SWAT vehicle during an active shooter training drill at Fairplex in Pomona, CA., Tuesday, April 24, 2018. The multi-agency scenario mimicked the mass shooting event in Las Vegas last October. (Staff photo by Jennifer Cappuccio Maher, Inland Valley Daily Bulletin/SCNG)

To make the scenario as realistic as possible, representatives from Moulage Concepts created realistic wounds and injuries.

“I want to see how this would all play out and I want to be helpful,” said Uzoma Happiness Nwanezi, 32, of Pomona, who volunteers at Pomona Valley Hospital. When she heard about the training, she wanted to be a part of it. “I am interested in how they train and how the hospital will react to things like this. I’ve never been a part of anything like this.”

To replicate the stress placed on Las Vegas emergency rooms, about 50 volunteers were bused to Pomona Valley Hospital. Others arrived in pickup trucks and other vehicles, not ambulances.

“During Las Vegas, hundreds of victims self-transported to area hospitals,” explained Rodriguez before the training session. “We want to recreate that situation.”

During the staged concert, which was simulated with a large mobile screen and sound system, several men armed with AR-15 rifles and handguns entered the rear of the grandstand area and began firing. During the confusion — with bullets popping and people running — a woman set off a bomb at the front of the venue injuring countless others.

The intricate scenario included wounded and injured concertgoers, venue staff and even one police officer. Officers arriving at the scene encountered people screaming for help, others running toward them trying to escape the gunfire and others barricaded in the rear of the venue.

Roberto Merza, 30, of Glendora also answered the call for volunteers. As a member of the Community Emergency Response Team, he hoped to gain a better insight on how to respond to mass casualty situations.

“It’s a great opportunity to see how first-responders do their thing while improving the skills I’ve learned,” he said as he sat in the “front row” of the concert waiting for the exercise to begin.

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Merza, Nwanezi and the other volunteers didn’t know until shortly before the training began, how seriously they were going to be hurt or if they survived the fictional ordeal. For Merza, that was as it should be, because there is no textbook active-shooter situation.

“We want there to be some confusion,” said one of the coordinators after one volunteer said she wasn’t clear on her role or where she should be. “We want this to be as real as possible.”

By the end of the two-hour drill, the shooting scene at Fairplex had been brought under control, with victims transported away, and the assailants neutralized by law enforcement. But the second part of the drill, helping the injured as the arrived at the “emergency room” for medical care, was just getting underway.

Beatriz E. Valenzuela is an award-winning journalist who’s covered breaking news in Southern California since 2006 and has been on the front lines of several national and international news events. She’s worked for media outlets serving Southern California readers covering education, local government, entertainment and all things nerd including comic book culture and video games. She’s an amateur obstacle course racer, constant fact-checker, mother of three and lover of all things adorable.